Minimally invasive surgery such as endoscopic surgery allows for major surgical operations to be performed with reduced pain and disability relative to conventional "open" surgery. In performing endoscopic surgery, the surgeon does not cut a large incision through the body wall to obtain access to the tissue requiring treatment. Instead, an endoscope, typically a miniaturized video camera, and certain specially-designed surgical instruments are inserted through a trocar tube or similar device. Trocar tubes, typically having a 5 mm to 10 mm inside diameter, produce only a small opening. The image provided by the endoscope is displayed on a large video screen or other type of monitor, thereby affording the surgeon enhanced visual control of the specially-designed instruments.
Endoscopic surgery is possible whenever a small optical instrument (endoscope) and miniaturized operating instruments can be inserted into the body cavity or other anatomical space. Such miniaturized operating instruments have been developed for endoscopic surgery in the abdomen ("laparoscopy"), in the chest ("thoracoscopy") and in joints ("arthroscopy").
For example, when performing a gallbladder removal, or cholecystectomy, utilizing minimally invasive surgery methods, a trocar is inserted through the umbilicus into the abdominal cavity. A laparoscope is then passed through the trocar in order to provide illumination and an enlarged video image of the inside portion of the abdomen. Additional trocars may be inserted through the abdominal wall to admit necessary instruments for performing the operation, and severing tissue. Severed tissues may also be extracted through these trocars. At the conclusion of the operation, all instruments and trocars are withdrawn from the abdominal wall and the puncture wounds are then sealed, often with only a bandage.
In performing both "open" and endoscopic surgical procedures, the surgeon must control bleeding that occurs when tissues are incised. Such bleeding obscures the surgeon's vision, reduces precision, and often necessitates slow and elaborate procedures to perform the surgery.
Controlling flow of blood from incised tissue is readily accomplished in "open" surgical procedures. The surgeon gains access to the target tissue by cutting large incisions through the body wall and displacing the overlying tissue to expose the tissue requiring treatment. A large opening is typically required to provide visibility and room to manipulate hands and instruments. Vital structures are held away from the operative site and shielded from inadvertent contact. The surgeon can directly touch and manipulate the various tissues. Bleeding from incised tissue is controlled by blotting or evacuating the accumulating blood. This step of removing the blood permits visual observation of the vessels for clamping or tying of those vessels to inhibit further blood loss.
In performing endoscopic surgery, the surgeon forgoes direct manual access to the tissue being operated upon. Consequently, traditional means of physically controlling bleeding (i.e., clamping and tying) are unavailable. Other techniques must then be employed to control bleeding during the surgical procedure. One such technique, which was first employed in "open" surgical procedures, is to thermally heat the bleeding tissue. Such thermal heating reduces the tendency of severed tissue to bleed. This process, referred to as "hemostasis," has been performed using at least two different endoscopic techniques to deposit sufficient heat in the tissue to reduce bleeding.
A first endoscopic technique provides hemostasis by converting laser light energy into heat. Lasers produce coherent light which can be transmitted via small-diameter fiber optic cables to the target tissue. Upon interaction with the tissue, the laser light is converted to heat. A disadvantage of this technique, besides the high initial cost of laser hardware, is that the depth of laser light absorption into the tissue. The depth of penetration of the laser light, and the heat produced thereby, varies from one type of tissue to another. Because lasers only transmit light in a straight line, thermal energy can be delivered to the tissue only for simple geometries.
Additionally, the amount of thermal energy delivered to the tissue can be a function of the separation distance between the tip of the fiber optic light guide and the tissue to be heated. This is a result of the defocusing of the light beam. The use of laser light in endoscopic surgery also interferes with the surgeon's visibility. For example, lasers may produce reflected or stray light which limits visibility. Also, because of the high temperatures that evolve from the absorbed laser light, these devices may generate smoke that further obscures visibility.
In order to circumvent some of the above disadvantages associated with shining laser light directly on tissue to accomplish hemostasis, laser light has also been employed to first heat a sapphire tip connected to the end of a fiber optic light guide. The tip is then brought into contact with the target tissue. A disadvantage of this technique is that the number of available geometric tip shapes is limited, thus limiting the usefulness of the technique. Furthermore, the technique still has a high initial cost for laser hardware and still produces smoke which limits visibility.
A second and older endoscopic technique for providing hemostasis, which was first developed for "open" surgery, employs passing an electric current through the tissue to generate the heat sufficient to coagulate or congeal the tissue. This technique is called "electrosurgery" and employs a high frequency power source called an electrosurgery unit. In monopolar electrosurgery, an active electrode is manipulated by the surgeon, while a passive electrode, in the shape of a plate, contacts the patient at a position remote from the surgical site. The electrosurgery unit supplies high frequency voltage between the two electrodes sufficient to cause an arc from the active electrode, to the most proximate least-resistive tissue, and through the patient to the passive electrode. The resulting current through the patient is converted to heat. Because the current density is highest adjacent to the active electrode and rapidly thereafter disperses throughout the patent's body, most of the heat is generated near the active electrode. This intense heat dehydrates the tissue and denatures the tissue proteins to form a coagulum that "seals" bleeding sites.
One of the principal disadvantages of the above technique, beside the fact that temperature is difficult to regulate, is that electrical current flows completely through the patient. Such current can follow non-localized and erratic paths and can therefore cause damage to non-targeted tissue both near and far away from the active electrode. Furthermore, the high voltage electrical current can also arc from the active electrode to other nearby non-targeted vital structures.
Monopolar electrosurgery, when employed in endoscopic surgery, can be especially dangerous since delicate vital structures, such as a bowel, cannot be physically pushed away or covered as in "open" surgery. Furthermore, since the surgeon's field of view is limited, sparks can arc outside the view of the video monitor to non-targeted vital tissue. This can result in injuries which may not even be detected at the time they are sustained. Such injuries are well documented and can result in high mortality rates.
Another potential disadvantage of monopolar electrosurgical techniques is the excessive tissue damage that can cause result from poor temperature control. Such damage can compromise wound healing and extend the time needed for patient recovery. Additionally, the procedure may produce vision-obscuring smoke, which must be evacuated.
In addition to the ability to provide hemostasis, endoscopic surgery requires the ability to remotely cut and dissect operative tissue. Ideally, such incisions should only occur in regions where it is desired to cut or dissect. However, since previously known endoscopic instruments must pass through tissue masses to gain access to operative sites, there is the potential that the cutting edges of the instrument may cause unwanted cuts to the overlying tissue while being moved to the operative site.
For "open surgery" it is known to provide surgical scalpels which employ a blade with an adjacent resistive heating element. The resistive heating element provides thermally-enhanced cutting, in addition to hemostasis, when electrical current is passed through the element. Although such resistive elements can be readily brought to a suitably high and constant temperature in air prior to contacting tissue, they rapidly cool when brought into contact with tissue. During "open" surgery, non-predictable and continually varying portions of the blade contact the tissue as it is being cut. As the blade cools, its ability to cut tissue and provide hemostasis becomes markedly less effective. Furthermore, tissue tends to adhere to the blade. If additional power is applied by conventional means to counteract this cooling, the additional power may be delivered to the uncooled portions of the blade, thus resulting in tissue damage and blade destruction.
Shaw U.S. Pat. No. 4,185,632 shows an improved surgical cutting instrument in which the temperature of the cutting portion of the blade is self-regulating. Radio frequency electrical currents maintain the temperature within an elevated preselected temperature range. These currents flow within variable skin depths in an electrical conductor disposed near the cutting edge of the blade. This variable skin depth effect produces self-regulation of the blade temperature.
In addition to the ability to provide hemostasis, and to remotely cut and dissect tissue, endoscopic surgery requires the use of instruments that reduce adherence of tissue to the instrument. Coagulum buildup and sticking limits the usefulness of the instrument and may cause undesirable tissue damage and bleeding. Also, the adherence of tissue to such surgical instruments limits the surgeon's control of the instrument.
It would therefore be desirable to provide a low cost hemostatic instrument for endoscopic surgery which has the ability to precisely control the location and quantity of thermal energy which is delivered to tissue.
It would also be desirable to provide such an instrument for endoscopic surgery that does not require electrical current to be conducted through the patient and consequently does not cause tissue damage in regions remote from the surgical site.
It would further be desirable to provide an endoscopic instrument that has the ability to provide localized and precise thermally-enhanced cutting of tissue.
It would still further be desirable to provide an endoscopic instrument which reduces the adherence of tissue and coagulum to the instrument so as to reduce tissue damage associated with such adherence and to maintain good thermal power delivery between the heating means and the tissue by reducing the thermal impedance associated with tissue or coagulum build up on said heating means.